The objectives of the study are twofold: (1) to continue the ongoing Phase III randomized polycythemia vera study and the associated "efficacy" studies and (2) to conduct a new Phase III randomized study of the myeloproliferative syndromes. By means of the major PVSG protocol the therapy amongst phlebotomy, radioactive phosphorus and chlorambucil will be selected as being optimum resulting in the least morbidity and the longest survival. The natural history of polycythemia vera will be characterized and the modifying effects of myelosuppressive therapy determined. Cytogenetic abnormalities are being detected by studies of the bone marrow and histopathologic marrow examinations are being performed. The myeloproliferative study proposes the most comprehensive analysis of myeloproliferative syndromes ever performed in patients. The purposes are 1) to characterize and re-classify the diagnostic criteria for these disorders in terms of clinical manifestations, morphologic abnormalities (blood and bone marrow), cytogenetics, blood chemistries and tests of hematopoietic function; 2) observe and record the "natural" history of these patients with respect to disease progression, incidence of transition to acute leukemia, etc.; 3) to compare the best available (drug, radiation and surgical) treatments specifically designed according to major clinical manifestation. The objectives will be pursued by the national cooperative group which is studying polycythemia vera; the present protocols are an extension of the interests of that group to other myeloproliferative disorders.